The invention is directed to a method and to an apparatus for controlling the output of sheets from input compartments of a sheet output means of a printer and copier device. The invention is also directed to a sheet output means for the implementation of the method which means comprises at least two input compartments, each having a means for removing a single sheet therefrom, a controller for actuating the means for removal and a sheet transfer means having a conveying path for transporting a sheet from the means for removal to the printing or copier device.
A plurality of input compartments in which sheets to be printed or other matter to be printed are inserted are usually provided in a sheet output means, particularly given high-performance printer and copier devices; and only "sheets" shall be mentioned below in this context. Sheets are taken from the input compartments and conveyed to processing devices of the printer and copier devices with conveyer means.
Thus, for example, JP-A-60-188 245 discloses a sheet output means for a copier device that is equipped with two input compartments for accepting sheets. A removal means with which an individual sheet can be respectively taken from the respective input compartment is provided at each input compartment. The removal means of the input compartments are actuated by a controller according to a predetermined sheet removal sequence. During operation of the sheet output means, the controller checks whether at least one of the input compartments is to be defined as nearly empty. As soon as one of the input compartments is defined as empty, only the removal means of the other input compartment that still contains enough sheets is activated by the controller. When both input compartments are almost empty, sheets are taken successively from both input compartments until the input compartments are empty.
A plurality of input compartments are not only provided in order to increase the capacity of a printer and copier means in that sheets can be successively taken from different input compartments as soon as the preceding compartment is empty, but also so that different printing matter, for example, differently colored sheets, sheets with a differently colored pre-print, sheets of a different format such as forms and the like, can be accommodated in the individual input compartments. For example, white sheets can be provided in one compartment, sheets provided with a company logo can be provided in a further compartment, personalized or color sheets can be provided in a third compartment etc.
Printing or copying jobs wherein different sheets must be accessed can thus be implemented with the assistance of a correspondingly designed control in that different input compartments are selected in a very specific sequence.
When a plurality of input compartments are provided in a sheet output means, then the transport paths for the individual input compartments of the sheet output means up to, for example, a sheet transfer location at which the sheets are output to the following printer and copier means differ in length. When the sheets are removed from the individual compartments in the same sequence in which they are processed, comparatively large distances, i.e. gaps, can derive between the individual sheets due to what are frequently transport paths of very different lengths.
In order to avoid such large gaps between individual sheets when conveying to the sheet transfer location or, respectively, to the printer and copier device, the transport paths of different length and the duration of a sheet transport from the individual compartments to the sheet transfer location that differs in length as a result thereof can be taken into consideration.
For example, a sheet from an input compartment from which a long transport path must be traversed up to the sheet transfer location can be removed earlier than a sheet from an input compartment from which a relatively short transport path must be traversed, even though the sheet removed later is processed before the sheet removed earlier.
The sequence in which the individual sheets are removed from the input compartments, which is referred to below as sheet removal sequence, can thus differ from the sequence in which the sheets are processed, which is referred to below as sheet processing sequence. As a result of an appropriately designed control, however, the distance between the individual sheets can be minimized or, respectively, an occurrence of large gaps can be avoided and, thus, the performance capability of high-performance printer and copier devices can be further-enhanced.
Even given an optimally designed control, however, problems can arise when a compartment is empty and this is discovered too late. When, for example, a sheet to be processed later in the processing sequence and that must cover a comparatively long transport path is removed from an input compartment earlier than a sheet to be processed earlier in the processing sequence and that must cover a comparatively short transport path, then the problem can occur that the sheet that is taken later from the corresponding compartment but is to be processed earlier in the processing sequence can no longer be taken since the corresponding input compartment is empty. In such an instance, the sheet processing sequence can no longer be adhered to.
The above problem is illustrated below with reference to a simple example (see FIG. 1). For the implementation of a printing job, sheets are needed from a compartment B and from a compartment D, these to be processed in the sequence B.sub.1 -B.sub.2 -D.sub.1. B.sub.1 thereby references a first sheet from the compartment B, B.sub.2 references a second sheet from the compartment B, and D.sub.1 references a sheet from the compartment D.
The compartment D is at a considerably greater distance from the sheet transfer location then the compartment B. For optimizing the printing and copying time, a removal sequence D.sub.1 -B.sub.1 -B.sub.2 is therefore expedient. It is also assumed that only one sheet is still present in the compartment B.
The device controller is then designed, for example, such that the sheet D.sub.1 is taken from the compartment D at the same point in time as the sheet B.sub.1 from the compartment B. Due to the assumption that only one sheet is still present in the compartment B, the compartment B is now empty. The second sheet B.sub.2 can thus no longer be taken from the compartment B and the processing sequence B.sub.1 -B.sub.2 -D.sub.1 can therefore also no longer be adhered to.
FIG. 2 shows a diagram of a device controller that sees to it that the processing sequence B.sub.1 -B.sub.2 -D.sub.1 is adhered to. To this end, the sheet output times or, respectively, points in time are entered on the ordinate in FIG. 2 and the path that a sheet must traverse from the respective compartment up to the sheet transfer location 10 (in FIG. 1) is entered on the abscissa.
As can be derived from the diagram in FIG. 2, the sheet B.sub.1, with reference to the zero point of the diagram is removed from the input compartment B after a time 1.5 s and is transported along a transport path b identified with a directional arrow. V B.sub.1 and HB.sub.1 thereby reference the leading or, respectively, trailing edge of the sheet B.sub.1. At time 2.3 s, the sheet B.sub.1 has reached the sheet transfer location 10 (FIG. 1), where the transport path b (0 mm) ends, as indicated on the abscissa of the diagram of FIG. 2.
In order to keep these spaces between the sheets to be printed in the processing sequence B.sub.1 -B.sub.2 -D.sub.1 as small as possible, the sheet D.sub.1 is removed from the input compartment D at the same point in time at which the sheet B.sub.1 was taken from the compartment B.
Due to the assumption that only one sheet is still present in the input compartment B, a sensor S allocated to the compartment B reports--after the sheet B.sub.1 has been taken--that the input compartment B is now empty. (For this reason, leading and trailing edge VB.sub.2 or, respectively, HB.sub.2 of the sheet B.sub.2 are merely shown with broken lines in FIG. 2.) This is detected at a point in time that corresponds to approximately 1.9 s on the ordinate.
At this time, however, the sheet D.sub.1 taken from the input compartment D is located, for example, at the location P on a transport path d identified by a directional arrow.
Since the compartment B is empty and a second sheet B.sub.2 can thus not be removed, the processing sequence B.sub.1 -B.sub.2 -D.sub.1 can also not be adhered to and the printer and copier means is or, respectively, must be stopped.
After the printer and copier means has been stopped, at least the sheets of a print job that have already been taken from the respective output compartments must be removed from the printer and copier device by the operating personnel. In the above-described exemplary case, this is the sheet D.sub.1. Over and above this, control problems in the following printing and copying operations can occur in that the controller does not know which sheets and how many sheets were removed from the printer and copier device by the operating personnel.